Japan Geoscience Union Meeting 2016

Presentation information

International Session (Oral)

Symbol S (Solid Earth Sciences) » S-TT Technology & Techniques

[S-TT18] Stress geomechanics: observations, modelings and implications

Sun. May 22, 2016 9:00 AM - 10:30 AM 302 (3F)

Convener:*HungYu Wu(Japan Agency for Marine-Earth Science and Technology), Chung-Han Chan(Earth Observatory of Singapore, Nanyang Technological University), Saneatsu Saito(Japan Agency for Marine-Earth Science and Technology), Yoshinori Sanada(Japan Agency for Marine-Earth Science and Technology), Ayumu Miyakawa(Geodynamics Research Group, Institute of Geology and Geoinformation (IGG), Geological Survey of Japan/AIST), Yasuhiro Yamada(Japan Agency for Marine-Earth Science and Technology (JAMSTEC), R&D Center for Ocean Drilling Science (ODS)), Chair:Chan Chung-Han(Earth Observatory of Singapore, Nanyang Technological University)

9:30 AM - 9:45 AM

[STT18-03] Effect of stress and fluid pressure change on shallow earthquake swarm induced by the 2011 Tohoku-Oki earthquake inferred from dense seismic observation

*Tomomi Okada1, Takashi NAKAYAMA1, Satoshi Hirahara1, Shuichiro Hori1, Toshiya Sato1, Toru Matsuzawa1 (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University)

Keywords:The 2011 Tohoku-Oki earthquake, Induced earthquake, stress, fluid pressure, focal mechanism

After the 2011 Tohoku-Oki earthquake, some earthquake swarms in the inland area have been occurring. As shown in previous studies, stress change and fluid pressure change would be the causes of the earthquake swarm. Coseismic change of stress tensors is thought to be caused by the stress change due to the Tohoku-Oki earthquake [e.g. Hasegawa et al., 2012; Yoshida et al., 2012]. Diversity of focal mechanisms, which could be interpreted with the Mohr circle, suggests high pore fluid pressure [e.g. Terakawa et al., 2012]. Temporal expansion of aftershock areas suggests that the increase in the fluid pressure is the cause of the earthquake swarm [e.g. Okada et al., 2015].
For understanding more details of the induced earthquake swarm and its causes, we deploy dense seismic observation networks in three areas: southern Akita, northern Akita, Fukushima (Aizu) -Yamagata [cf. Hirahara et al., 2015, AGU Fall Meeting]. Station separation is less than a couple of kilometers in southern Akita, and about 5 kilometers in northern Akita and Fukushima-Yamagata areas. Seismometers and data loggers deployed are KVS-300 and EDR-X7000 of Kinkei System Corporation, respectively.
By using data from the dense seismic network, we can determine reliable focal mechanisms even for M~1 earthquakes. Focal depths of most of earthquakes are determined to be a few kilometers shallower than JMA catalog depths. The improvements of hypocenter locations and focal mechanisms will enable us to estimate the stress regime and the fluid pressure in Tohoku district in more details.
This study was conducted with the support of the Grant-in-Aid for Scientific Research on Innovative Areas (Crustal Dynamics, KAKENHI No. 26109002) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. This study was also supported by the MEXT under its Earthquake and Volcano Hazards Observation and Research Program. Dr. Takahiro Shi’ina, Dr. Keisuke Yoshida, and Mr. Yukihiko Chiba helped us for the observation.